let s = "aabcd",t = "aabcde"
var findTheDifference = function(s, t) {
    let ret = 0;
    for (const ch of s) {
        ret ^= ch.charCodeAt();
    }
    for (const ch of t) {
        ret ^= ch.charCodeAt();
    }
    console.log(ret);
    
    return String.fromCharCode(ret);
};
console.log(findTheDifference(s,t));
